The present invention relates to complexes of transition metals or alkaline earth-metals which are capable of combusting to generate gases. More particularly, the present invention relates to providing such complexes which rapidly oxidize to produce significant quantities of gases, particularly water vapor and nitrogen.
Gas generating chemical compositions are useful in a number of different contexts. One important use for such compositions is in the operation of xe2x80x9cair bags.xe2x80x9d Air bags are gaining in acceptance to the point that many, if not most, new automobiles are equipped with such devices. Indeed, many new automobiles are equipped with multiple air bags to protect the driver and passengers.
In the context of automobile air bags, sufficient gas must be generated to inflate the device within a fraction of a second. Between the time the car is impacted in an accident, and the time the driver would otherwise be thrust against the steering wheel, the air bag must fully inflate. As a consequence, nearly instantaneous gas generation is required.
There are a number of additional important design criteria that must be satisfied. Automobile manufacturers and others have set forth the required criteria which must be met in detailed specifications. Preparing gas generating compositions that meet these important design criteria is an extremely difficult task. These specifications require that the gas generating composition produce gas at a required rate. The specifications also place strict limits on the generation of toxic or harmful gases or solids. Examples of restricted gases include carbon monoxide, carbon dioxide, NOx, SOx, and hydrogen sulfide.
The gas must be generated at a sufficiently and reasonably low temperature so that an occupant of the car is not burned upon impacting an inflated air bag. If the gas produced is overly hot, there is a possibility that the occupant of the motor vehicle may be burned upon impacting a just deployed air bag. Accordingly, it is necessary that the combination of the gas generant and the construction of the air bag isolates automobile occupants from excessive heat. All of this is required while the gas generant maintains an adequate burn rate.
Another related but important design criteria is that the gas generant composition produces a limited quantity of particulate materials. Particulate materials can interfere with the operation of the supplemental restraint system, present an inhalation hazard, irritate the skin and eyes, or constitute a hazardous solid waste that must be dealt with after the operation of the safety device. In the absence of an acceptable alternative, the production of irritating particulates is one of the undesirable, but tolerated aspects of the currently used sodium azide materials.
In addition to producing limited, if any, quantities of particulates, it is desired that at least the bulk of any such particulates be easily filterable. For instance, it is desirable that the composition produce a filterable slag. If the reaction products form a filterable material, the products can be filtered and prevented from escaping into the surrounding environment.
Both organic and inorganic materials have been proposed as possible gas generants. Such gas generant compositions include oxidizers and fuels which react at sufficiently high rates to produce large quantities of gas in a fraction of a second.
At present, sodium azide is the most widely used and currently accepted gas generating material. Sodium azide nominally meets industry specifications and guidelines.
Nevertheless, sodium azide presents a number of persistent problems. Sodium azide is highly toxic as a starting material, since its toxicity level as measured by oral rat LD50 is in the range of 45 mg/kg. Workers who regularly handle sodium azide have experienced various health problems such as severe headaches, shortness of breath, convulsions, and other symptoms.
In addition, no matter what auxiliary oxidizer is employed, the combustion products from a sodium azide gas generant include caustic reaction products such as sodium oxide, or sodium hydroxide. Molybdenum disulfide or sulfur have been used as oxidizers for sodium azide. However, use of such oxidizers results in toxic products such as hydrogen sulfide gas and corrosive materials such as sodium oxide and sodium sulfide. Rescue workers and automobile occupants have complained about both the hydrogen sulfide gas and the corrosive powder produced by the operation of sodium azide-based gas generants.
Increasing problems are also anticipated in relation to disposal of unused gas-inflated supplemental restraint systems, e.g. automobile air bags, in demolished cars. The sodium azide remaining in such supplemental restraint systems can leach out of the demolished car to become a water pollutant or toxic waste. Indeed, some have expressed concern that sodium azide might form explosive heavy metal azides or hydrazoic acid when contacted with battery acids following disposal.
Sodium azide-based gas generants are most commonly used for air bag inflation, but with the significant disadvantages of such compositions many alternative gas generant compositions have been proposed to replace sodium azide. Most of the proposed sodium azide replacements, however, fail to deal adequately with all of the criteria set forth above.
It will be appreciated, therefore, that there are a number of important criteria for selecting gas generating compositions for use in automobile supplemental restraint systems. For example, it is important to select starting materials that are not toxic. At the same time, the combustion products must not be toxic or harmful. In this regard, industry standards limit the allowable amounts of various gases and particulates produced by the operation of supplemental restraint systems.
It would, therefore, be a significant advance to provide compositions capable of generating large quantities of gas that would overcome the problems identified in the existing art. It would be a further advance to provide a gas generating composition which is based on substantially nontoxic starting materials and which produces substantially nontoxic reaction products. It would be another advance in the art to provide a gas generating composition which produces very limited amounts of toxic or irritating particulate debris and limited undesirable gaseous products. It would also be an advance to provide a gas generating composition which forms a readily filterable solid slag upon reaction.
Such compositions and methods for their use are disclosed and claimed herein.
The present invention is related to the use of complexes of transition metals or alkaline earth metals as gas generating compositions. These complexes are comprised of a metal cation and a neutral ligand containing hydrogen and nitrogen. One or more oxidizing anions are provided to balance the charge of the complex. Examples of typical oxidizing anions which can be used include nitrates, nitrites, chlorates, perchlorates, peroxides, and superoxides. In some cases the oxidizing anion is part of the metal cation coordination complex. The complexes are formulated such that when the complex combusts, a mixture of gases containing nitrogen gas and water vapor are produced. A binder can be provided to improve the crush strength and other mechanical properties of the gas generant composition. A co-oxidizer can also be provided primarily to permit efficient combustion of the binder. Importantly, the production of undesirable gases or particulates is substantially reduced or eliminated.
Specific examples of the complexes used herein include metal nitrite ammines, metal nitrate ammines, metal perchlorate ammines, metal nitrite hydrazines, metal nitrate hydrazines, metal perchlorate hydrazines, and mixtures thereof.
The complexes within the scope of the present invention rapidly combust or decompose to produce significant quantities of gas.
The metals incorporated within the complexes are transition metals, alkaline earth metals, metalloids, or lanthanide metals that are capable of forming ammine or hydrazine complexes. The presently preferred metal is cobalt. Other metals which also form complexes with the properties desired in the present invention include, for example, magnesium, manganese, nickel, titanium, copper, chromium, zinc, and tin. Examples of other usable metals include rhodium, iridium, ruthenium, palladium, and platinum. These metals are not as preferred as the metals mentioned above, primarily because of cost considerations.
The transition metal cation or alkaline earth metal cation acts as a template at the center of the coordination complex. As mentioned above, the complex includes a neutral ligand containing hydrogen and nitrogen. Currently preferred neutral ligands are NH3 and N2H4. One or more oxidizing anions may also be coordinated with the metal cation. Examples of metal complexes within the scope of the present invention include Cu(NH3)4(NO3)2 (tetraamminecopper(II) nitrate), Co(NH3)3(NO2)3 (trinitrotriamminecobalt(III)), Co(NH3)6(Cl4)3 (hexaamminecobalt(III) perchlorate), Co(NH3)6 (NO3)3 (hexaamminecobalt(III) nitrate), Zn(N2H4)3(NO3)2 (tris-hydrazine zinc nitrate), Mg(N2H4)2(ClO4)2 (bis-hydrazine magnesium perchlorate), and Pt(NO2)2(NH2NH2)2 (bis-hydrazine platinum(II) nitrite).
It is within the scope of the present invention to include metal complexes which contain a common ligand in addition to the neutral ligand. A few typical common ligands include: aquo (H2O), hydroxo (OH), carbonato (CO3), oxalato (C2O4), cyano (CN), isocyanato (NC), chloro (Cl), fluoro (F), and similar ligands. The metal complexes within the scope of the present invention are also intended to include a common counter ion, in addition to the oxidizing anion, to help balance the charge of the complex. A few typical common counter ions include: hydroxide (OHxe2x88x92), chloride (Clxe2x88x92), fluoride (Fxe2x88x92), cyanide (CNxe2x88x92), carbonate (CO3xe2x88x922), phosphate (PO4xe2x88x923), oxalate (C2O4xe2x88x922), borate (BO4xe2x88x925), ammonium (NH4+), and the like.
It is observed that metal complexes containing the described neutral ligands and oxidizing anions combust rapidly to produce significant quantities of gases. Combustion can be initiated by the application of heat or by the use of conventional igniter devices.
As discussed above, the present invention is related to gas generant compositions containing complexes of transition metals or alkaline earth metals. These complexes are comprised of a metal cation template and a neutral ligand containing hydrogen and nitrogen. One or more oxidizing anions are provided to balance the charge of the complex. In some cases the oxidizing anion is part of the coordination complex with the metal cation. Examples of typical oxidizing anions which can be used include nitrates, nitrites, chlorates, perchlorates, peroxides, and superoxides. The complexes can be combined with a binder or mixture of binders to improve the crush strength and other mechanical properties of the gas generant composition. A co-oxidizer can be provided primarily to permit efficient combustion of the binder.
Metal complexes which include at least one common ligand in addition to the neutral ligand are also included within the scope of the present invention. As used herein, the term common ligand includes well known ligands used by inorganic chemists to prepare coordination complexes with metal cations. The common ligands are preferably polyatomic ions or molecules, but some monoatomic ions, such as halogen ions, may also be used. Examples of common ligands within the scope of the present invention include aquo (H2O), hydroxo (OH), perhydroxo (O2H), peroxo (O2), carbonato (CO3), oxalato (C2O4), carbonyl (CO), nitrosyl (NO), cyano (CN), isocyanato (NC), isothiocyanato (NCS), thiocyanato (SCN), chloro (Cl), fluoro (F), amido (NH2), imdo (NH), sulfato (SO4), phosphato (PO4), ethylenediaminetetraacetic acid (EDTA), and similar ligands. See, F. Albert Cotton and Geoffrey Wilkinson, Advanced Inorganic Chemistry, 2nd ed., John Wiley and Sons, pp. 139-142, 1966 and James E. Huheey, Inorganic Chemistry, 3rd ed., Harper and Row, pp. A-97-A-107, 1983, which are incorporated herein by reference. Persons skilled in the art will appreciate that suitable metal complexes within the scope of the present invention can be prepared containing a neutral ligand and another ligand not listed above.
In some cases, the complex can include a common counter ion, in addition to the oxidizing anion, to help balance the charge of the complex. As used herein, the term common counter ion includes well known anions and cations used by inorganic chemists as counter ions. Examples of common counter ions within the scope of the present invention include hydroxide (OHxe2x88x92), chloride (Clxe2x88x92), fluoride (Fxe2x88x92), cyanide (CNxe2x88x92), thiocyanate (SCNxe2x88x92), carbonate (CO3xe2x88x922), sulfate (SO4xe2x88x922), phosphate (PO4xe2x88x923), oxalate (C2O4xe2x88x922), borate (BO4xe2x88x925), ammonium (NH4+), and the like. See, Whitten, K. W., and Gailey, K. D., General Chemistry, Saunders College Publishing, p. 167, 1981 and James E. Huheey, Inorganic Chemistry, 3rd ed., Harper and Row, pp. A-97-A-103, 1983, which are incorporated herein by reference.
The gas generant ingredients are formulated such that when the composition combusts, nitrogen gas and water vapor are produced. In some cases, small amounts of carbon dioxide or carbon monoxide are produced if a binder, co-oxidizer, common ligand or oxidizing anion contain carbon. The total carbon in the gas generant composition is carefully controlled to prevent excessive generation of CO gas. The combustion of the gas generant takes place at a rate sufficient to qualify such materials for use as gas generating compositions in automobile air bags and other similar types of devices.
Importantly, the production of other undesirable gases or particulates is substantially reduced or eliminated.
Complexes which fall within the scope of the present invention include metal nitrate ammines, metal nitrite ammines, metal perchlorate ammines, metal nitrite hydrazines, metal nitrate hydrazines, metal perchlorate hydrazines, and mixtures thereof. Metal ammine complexes are defined as coordination complexes including ammonia as the coordinating ligand. The ammine complexes can also have one or more oxidizing anions, such as nitrite (NO2xe2x88x92), nitrate (NO3xe2x88x92), chlorate (ClO3xe2x88x92), perchlorate (ClO4xe2x88x92), peroxide (O22xe2x88x92), and super-oxide (O2xe2x88x92), or mixtures thereof, in the complex. The present invention also relates to similar metal hydrazine complexes containing corresponding oxidizing anions.
It is suggested that during combustion of a complex containing nitrite and ammonia groups, the nitrite and ammonia groups undergo a diazotization reaction. This reaction is similar, for example, to the reaction of sodium nitrite and ammonium sulfate, which is set forth as follows:
2NaNO2+(NH4)2SO4xe2x86x92Na2SO4+4H2O+2N2
Compositions such as sodium nitrite and ammonium sulfate in combination have little utility as gas generating substances. These materials are observed to undergo metathesis reactions which result in unstable ammonium nitrite. In addition, most simple nitrite salts have limited stability.
In contrast, the metal complexes used in the present invention are stable materials which, in certain instances, are capable of undergoing the type of reaction set forth above. The complexes of the present invention also produce reaction products which include desirable quantities of nontoxic gases such as water vapor and nitrogen. In addition, a stable metal, or metal oxide slag is formed. Thus, the compositions of the present invention avoid several of the limitations of existing sodium azide gas generating compositions.
Any transition metal, alkaline earth metal, metalloid, or lanthanide metal which is capable of forming the complexes described herein is a potential candidate for use in these gas generating compositions. However, considerations such as cost, reactivity, thermal stability, and toxicity may limit the most preferred group of metals.
The presently preferred metal is cobalt. Cobalt forms stable complexes which are relatively inexpensive. In addition, the reaction products of cobalt complex combustion are relatively nontoxic. Other preferred metals include magnesium, manganese, copper, zinc, and tin. Examples of less preferred but usable metals include nickel, titanium, chromium, rhodium, iridium, ruthenium, and platinum.
A few representative examples of ammine complexes within the scope of the present invention, and the associated gas generating decomposition reactions are as follows:
Cu (NH3)2(NO2)2xe2x86x92CuO+3H2O+2N2
2Co(NH3)3(NO2)3 xe2x86x922CoO+9H2O+6N2+xc2xdO2
2Cr(NH3)3(NO2)3xe2x86x92Cr2O3+9H2O+6N2
[Cu(NH3)4](NO3)2xe2x86x92Cu+3N2+6H2O
2B+3Co(NH3)6Co(NO2)6 xe2x86x926CoO+B2O3+27H2O+18N2
Mg+Co(NH3)4(NO2)2Co(NH3)2(NO2)4 xe2x86x922CoO+MgO+9H2O+6N2
xe2x80x8310[Co(NH3)4(NO2)2](NO2)+2Sr(NO3)2xe2x86x9210CoO+2SrO+37N2+60H2O
18[Co(NH3)6](NO3)3+4Cu2 (OH)3NO3 xe2x86x9218CoO+8Cu+83N2168H2O+
2 [Co(NH3)6](NO3)3+2NH4NO3xe2x86x922CoO+11N2+22H2O+N2
TiCl4(NH3)2+3BaO2xe2x86x92TiO2+2BaCl2+BaO+3H2O+N2
4[Cr(NH3)5OH](ClO4)2+[SnCl4(NH3)2]xe2x86x924CrCl3+SnO +35H2O+11N2
10[Ru(NH3)5N2](NO3)2+3Sr(NO3)2 xe2x86x923SrO+10Ru+48N2+75H2O
[Ni(H2O)2(NH3)4](NO3)2xe2x86x92Ni+3N2+8H2O
2 [Cr(O2)2(NH3)3]+4NH4NO3 xe2x86x927N2+17H2O+Cr2O3
[Ni(CN)2(NH3)]*C6H6+43KClO4xe2x86x928NiO+43KCl+64CO2+12N2+36H2O
2[Sm(O2)3]Gd(NH3)9](ClO4)3xe2x86x92Sm2O3+4GdCl3+19N2+57H2O
2Er(NO3)3(NH3)3+2[Co(NH3)6](NO3)3xe2x86x92Er2O3+12CoO+60N2+117H2O
A few representative examples of hydrazine complexes within the scope of the present invention, and related gas generating reactions are: as follows:
5Zn(N2H4)(NO3)2+Sr(NO3)2xe2x86x925ZnO+21N2+30H2O+SrO
Co(N2H4)3(NO3)2xe2x86x92Co+4N2+6H2O
3Mg(N2H4)2(ClO4)2+2Si3N4xe2x86x926SiO2+3MgCl2+10N2+12H2O
2Mg(N2H4)2(NO3)2+2[Co(NH3)4(NO2)2]NO2xe2x86x922MgO+2CoO+13N2+20H2O+20H2O
Pt(NO2)2(N2H4)2xe2x86x92Pt+3N2+4H2O
xe2x80x83[Mn(N2H4)3](NO3)2+Cu (OH)2xe2x86x92Cu+MnO+4N2+7H2O
2[La(N2H4)4(NO3)](NO3)2+NH4NO3xe2x86x92La2O3+12N2+18H2O
While the complexes of the present invention are relatively stable, it is also simple to initiate the combustion reaction. For example, if the complexes are contacted with a hot wire, rapid gas producing combustion reactions are observed. Similarly, it is possible to initiate the reaction by means of conventional igniter devices. One type of igniter device includes a quantity of B/KNO3 granules or pellets which is ignited, and which in turn is capable of igniting the compositions of the present invention. Another igniter device includes a quantity of Mg/Sr(NO3)2/nylon granules.
It is also important to note that many of the complexes defined above undergo xe2x80x9cstoichiometricxe2x80x9d decomposition. That is, the complexes decompose without reacting with any other material to produce large quantities of nitrogen and water, and a metal or metal oxide. However, for certain complexes it may be desirable to add a fuel or oxidizer to the complex in order to assure complete and efficient reaction. Such fuels include, for example, boron, magnesium, aluminum, hydrides of boron or aluminum, carbon, silicon, titanium, zirconium, and other similar conventional fuel materials, such as conventional organic binders. Oxidizing species include nitrates, nitrites, chlorates, perchlorates, peroxides, and other similar oxidizing materials. Thus, while stoichiometric decomposition is attractive because of the simplicity of the composition and reaction, it is also possible to use complexes for which stoichiometric decomposition is not possible.
As mentioned above, nitrate and perchlorate complexes also fall within the scope of the invention. A few representative examples of such nitrate complexes include: Co(NH3)6(NO3)3Cu(NH3)4 (NO3)2, [(Co(NH3)5(NO3)](NO3)2, [(Co(NH3)(NO2)](NO3)2, [(Co(NH3)5(H2O)](NO3)2. A few representative examples of perchlorate complexes within the scope of the invention include: [Co(NH3)6](ClO4)3, [Co(NH3)5(NO2)]ClO4, [Mg(N2H4)2](ClO4)2.
Preparation of metal nitrite or nitrate ammine complexes of the present invention is described in the literature. Specifically, reference is made to Hagel et al., xe2x80x9cThe Triamines of Cobalt (III). I. Geometrical Isomers of Trinitrotriamminecobalt (III),xe2x80x9d 9 Inorganic Chemistry 1496 (June 1970); G. Pass and H. Sutcliffe, Practical Inorganic Chemistry, 2nd Ed., Chapman and Hull, New York, 1974; Shibata et al., xe2x80x9cSynthesis of Nitroammine- and Cyanoamminecobalt(III) Complexes With Potassium Tricarbonatocobaltate(III) as the Starting Material,xe2x80x9d 3 Inorganic Chemistry 1573 (Nov. 1964); Wieghardt et al., xe2x80x9cxcexc-Carboxylatodi-xcexc-hydroxo-bis[triamminecobalt(III)]Complexes,xe2x80x9d 23 Inorganic Synthesis 23 (1985); Laing, xe2x80x9cmer- and fac-[Co(NH3)3NO2)3]: Do They Exist?xe2x80x9d 62 J. Chem Educ., 707 (1985); Siebert, xe2x80x9cIsomere des Trinitrotriamminkobalt (III),xe2x80x9d 441 Z. Anorg. Allq. Chem. 47 (1978); all of which are incorporated herein by this reference. Transition metal perchlorate ammine complexes are synthesized by similar methods. As mentioned above, the ammine complexes of the present invention are generally stable and safe for use in preparing gas generating formulations.
Preparation of metal perchlorate, nitrate, and nitrite hydrazine complexes is also described in the literature. Specific reference is made to Patil et al., xe2x80x9cSynthesis and Characterisation of Metal Hydrazine Nitrate, Azide, and Perchlorate Complexes,xe2x80x9d 12 Synthesis and Reactivity In Inorganic and Metal Organic Chemistry, 383 (1982); Klyichnikov et al., xe2x80x9cPreparation of Some Hydrazine Compounds of Palladium,xe2x80x9d 13 Russian Journal of Inorganic Chemistry, 416 (1968); Klyichnikov et al., xe2x80x9cConversion of Mononuclear Hydrazine Complexes of Platinum and Palladium Into Binuclear Complexes,xe2x80x9d 36 Ukr. Khim. Zh., 687 (1970).
The described complexes can be processed into usable granules or pellets for use in gas generating devices. Such devices include automobile air bag supplemental restraint systems. Such gas generating compositions will comprise a quantity of the described complexes and preferably, a binder and a co-oxidizer. The compositions produce a mixture of gases, principally nitrogen and water vapor, upon decomposition or burning. The gas generating device will also include means for initiating the burning of the composition, such as a hot wire or igniter. In the case of an automobile air bag system, the system will include the compositions described above; a collapsed, inflatable air bag; and means for igniting said gas-generating composition within the air bag system. Automobile air bag systems are well known in the art.
Typical binders used in the gas generating compositions of the present invention include binders conventionally used in propellant, pyrotechnic and explosive compositions including, but not limited to, lactose, boric acid, silicates including magnesium silicate, polypropylene carbonate, polyethylene glycol, naturally occurring gums such as guar gum, acacia gum, modified celluloses and starches (a detailed discussion of such gums is provided by C. L. Mantell, The Water-Soluble Gums, Reinhold Publishing Corp., 1947, which is incorporated herein by reference), polyacrylic acids, nitrocellulose, polyacrylamide, polyamides, including nylon, and other conventional polymeric binders. Such binders improve mechanical properties or provide enhanced crush strength. Although water immiscible binders can be used in the present invention, it is currently preferred to use water soluble binders. The binder concentration is preferably in the range from 0.5 to 12% by weight, and more preferably from 2% to 8% by weight of the gas generant composition.
Applicants have found that the addition of carbon such as carbon black or activated charcoal to gas generant compositions improves binder action significantly perhaps by reinforcing the binder and thus, forming a micro-composite. Improvements in crush strength of 50% to 150% have been observed with the addition of carbon black to compositions within the scope of the present invention. Ballistic reproducibility is enhanced as crush strength increases. The carbon concentration is preferably in the range of 0.1% to 6% by weight, and more preferably from 0.3 to 3% by weight of the gas generant composition.
The co-oxidizer can be a conventional oxidizer such as alkali, alkaline earth, lanthanide, or ammonium perchlorates, chlorates, peroxides, nitrites, and nitrates, including for example, Sr(NO3)2, NH4ClO4, KNO3, and (NH4)2Ce(NO3)6.
The co-oxidizer can also be a metal containing oxidizing agent such as metal oxides, metal hydroxides, metal peroxides, metal oxide hydrates, metal oxide hydroxides, metal hydrous oxides, and mixtures thereof, including those described in U.S. Pat. No. 5,439,537 issued Aug. 8, 1995, titled xe2x80x9cThermite Compositions for Use as Gas Generants,xe2x80x9d which is incorporated herein by reference. Examples of metal oxides include, among others, the oxides of copper, cobalt, manganese, tungsten, bismuth, molybdenum, and iron, such as CuO, Co2O3, Co3O4, CoFe2O4, Fe2O3, MoO3, Bi2MoO6, and Bi2O3. Examples of metal hydroxides include, among others, Fe(OH)3, Co(OH)3, Co(OH)2, Ni(OH)2, Cu(OH)2, and Zn(OH)2. Examples of metal oxide hydrates and metal hydrous oxides include, among others, Fe2O3 xc2x7xH2O, SnO2xc2x7xH2O, and MoO3xc2x7H2O. Examples of metal oxide hydroxides include, among others, CoO(OH)2, FeO(OH)2, MnO(OH)2and MnO(OH)3.
The co-oxidizer can also be a basic metal carbonate such as metal carbonate hydroxides, metal carbonate oxides, metal carbonate hydroxide oxides, and hydrates and mixtures thereof and a basic metal nitrate such as metal hydroxide nitrates, metal nitrate oxides, and hydrates and mixtures thereof, including those oxidizers described in U.S. Pat. No. 5,429,691, titled xe2x80x9cThermite Compositions for use as Gas Generants,xe2x80x9d which is incorporated herein by reference.
Table 1, below, lists examples of typical basic metal carbonates capable of functioning as co-oxidizers in the compositions of the present invention:
Table 2, below, lists examples of typical basic metal nitrates capable of functioning as co-oxidizers in the compositions of the present invention:
In certain instances it will also be desirable to use mixtures of such oxidizing agents in order to enhance ballistic properties or maximize filterability of the slag formed from combustion of the composition.
The present compositions can also include additives conventionally used in gas generating compositions, propellants, and explosives, such as burn rate modifiers, slag formers, release agents, and additives which effectively remove NOx. Typical burn rate modifiers include Fe2O3, K2B12H12, Bi2MoO6, and graphite carbon powder or fibers. A number of slag forming agents are known and include, for example, clays, talcs, silicon oxides, alkaline earth oxides, hydroxides, oxalates, of which magnesium carbonate, and magnesium hydroxide are exemplary. A number of additives and/or agents are also known to reduce or eliminate the oxides of nitrogen from the combustion products of a gas generant composition, including alkali metal salts and complexes of tetrazoles, aminotetrazoles, triazoles and related nitrogen heterocycles of which potassium aminotetrazole, sodium carbonate and potassium carbonate are exemplary. The composition can also include materials which facilitate the release of the composition from a mold such as graphite, molybdenum sulfide, calcium stearate, or boron nitride.
Typical ignition aids/burn rate modifiers which can be used herein include metal oxides, nitrates and other compounds such as, for instance, Fe2O3, K2B12H12xc2x7H2O, BiO(NO3), Co2O3, CoFe2O4, CuMoO4, Bi2MoO6, MnO2, Mg(NO3)2xc2x7xH2O, Fe(NO3)xc2x7xH2O, Co(NO3)2xc2x7xH2O, and NH4NO3. Coolants include magnesium hydroxide, cupric oxalate, boric acid, aluminum hydroxide, and silicotungstic acid. Coolants such as aluminum hydroxide and silicotungstic acid can also function as slag enhancers.
It will be appreciated that many of the foregoing additives may perform multiple functions in the gas generant formulation such as a co-oxidizer or as a fuel, depending on the compound. Some compounds may function as a co-oxidizer, burn rate modifier, coolant, and/or slag former.
Several important properties of typical hexaamminecobalt (III) nitrate gas generant compositions within the scope of the present invention have been compared with those of commercial sodium azide gas generant compositions. These properties illustrate significant differences between conventional sodium azide gas generant compositions and gas generant compositions within the scope of the present invention. These properties are summarized below:
The term xe2x80x9cgas fraction of generantxe2x80x9d means the weight fraction of gas generated per weight of gas generant. Typical hexaamminecobalt(III) nitrate gas generant compositions have more preferred flame temperatures in the range from 1850xc2x0 K. to 1900xc2x0 K., gas fraction of generant in the range from 0.70 to 0.75, total carbon content in the generant in the range from 1.5% to 3.0% burn rate of generant at 1000 psi in the range from 0.2 ips to 0.35 ips, and surface area of generant in the range from 2.5 cm2/g to 3.5 cm2/g.
The gas generating compositions of the present invention are readily adapted for use with conventional hybrid air bag inflator technology. Hybrid inflator technology is based on heating a stored inert gas (argon or helium) to a desired temperature by burning a small amount of propellant. Hybrid inflators do not require cooling filters used with pyrotechnic inflators to cool combustion gases, because hybrid inflators are able to provide a lower temperature gas. The gas discharge temperature can be selectively changed by adjusting the ratio of inert gas weight to propellant weight. The higher the gas weight to propellant weight ratio, the cooler the gas discharge temperature.
A hybrid gas generating system comprises a pressure tank having a rupturable opening, a pre-determined amount of inert gas disposed within that pressure tank; a gas generating device for producing hot combustion gases and having means for rupturing the rupturable opening; and means for igniting the gas generating composition. The tank has a rupturable opening which can be broken by a piston when the gas generating device is ignited. The gas generating device is configured and positioned relative to the pressure tank so that hot combustion gases are mixed with and heat the inert gas. Suitable inert gases include, among others, argon, helium and mixtures thereof. The mixed and heated gases exit the pressure tank through the opening and ultimately exit the hybrid inflator and deploy an inflatable bag or balloon, such as an automobile air bag.
Preferred embodiments of the invention yield combustion products with a temperature greater than about 1800xc2x0 K., the heat of which is transferred to the cooler inert gas causing a further improvement in the efficiency of the hybrid gas generating system.
Hybrid gas generating devices for supplemental safety restraint application are described in Frantom, Hybrid Airbag Inflator Technology, Airbag Int""l Symposium on Sophisticated Car Occupant Safety Systems, (Weinbrenner-Saal, Germany, Nov. 2-3, 1992).